Implantable pumps are used for a variety of medical purposes for pumping bodily fluids such as blood. For example, when the output of the heart is insufficient to meet the circulatory needs of a person or animal, a pump can be implanted to boost circulation.
The pump can be implanted within the human body to augment the blood flow from the left ventricle of the heart to the body in patients with diminished heart function, such pumps being referred to as left ventricular assist devices (“LVADs”).
Referring to FIG. 1, a general description of a blood pump within a system for pumping blood can be as found in United States Pre-Grant Publication 2014/0073837 entitled “Blood Flow System with Variable Speed Control,” the disclosure of which is incorporated by reference herein. System 100 includes a housing 110 surrounding a rotational drive assembly including motor 120 and fluid drive element 130 such as impeller 131. In some embodiments, system 100 comprises a rotational drive assembly similar to that described in U.S. Pat. No. 6,116,862 entitled “Blood Pump”, or U.S. Pat. No. 6,176,848 entitled “Intravascular Blood Pump”, the disclosures of said patents also being incorporated by reference herein. Impeller 131, is magnetically coupled with and rotated by a spinning drive mechanism 120 having a set of magnetic poles 152 coupled across gap 112 with corresponding magnetic poles 154 of the impeller 131 through force of magnetic attraction. Drive mechanism 120 includes a motor (not shown) which rotates poles 152 around the common axis 137 of the drive motor and impeller. A supporting element such as a shaft 121 extending through a central opening 114 can support the impeller while the impeller is rotating and held in place axially by the magnetic attraction from the drive mechanism 120. The pump chamber 115 includes the open space between a tubular portion of the housing 110 and other components of the pump such as impeller 131, shaft 121 and motor 120. In some embodiments, the chamber 115 comprises a volume less than 100 mL, for example less than 50 mL. In some embodiments, chamber 115 comprises a volume less than 10 mL, for example less than 5 mL, such as less than 2.5 mL or less than 1.2 mL.
Housing 110 comprises two ports, inlet port 116 and outlet port 117. When impeller 131 is rotated, fluid propulsion forces are generated such that fluid flows from inlet port 116 to outlet port 117 through chamber 115. A hollow tube, inlet cannula 160 includes proximal end 163, distal end 164 and lumen 161 therebetween. Inlet cannula 160 is attached and/or is attachable to inlet port 116 at its distal end 164, such as via a compression fitting 162. In some embodiments, proximal end 163 of inlet cannula 160 is configured to be fluidly attached to a source of blood, such as a source of oxygenated blood, such as at the left ventricle of a patient. In some embodiments, inlet cannula 160 can be configured as described in U.S. patent application Ser. No. 12/392,623, entitled “Devices, Methods and Systems for Establishing Supplemental Blood Flow in the Circulatory System”, published as U.S. Pre-Grant Publication No. 2009/0182188, the disclosure of which is incorporated herein by reference.
A second hollow tube, outlet cannula 170 includes proximal end 173, distal end 174 and lumen 171 therebetween. Outlet cannula 170 is attached and/or is attachable to outlet port 117, such as via a compression fitting 172. In embodiments wherein inlet cannula 160 is attached to a source of arterial blood, distal end 174 of outlet cannula 170 can be configured to be fluidly attached to a blood vessel, such as an artery, such as via an anastomosis. In some embodiments, outlet cannula 170 can comprise an anastomotic connector on its distal end 174, such as is described in U.S. Pat. No. 8,333,727, entitled “Two Piece Endovascular Anastomotic Connector”, the disclosure of which is incorporated herein by reference.
Housing 110, inlet cannula 160 and outlet cannula 170 are typically implanted in the patient, while other components such as control module 150 can be implanted in the patient, or can be coupled with motor 120 via a percutaneous cable 151. In some embodiments, impeller 131 and motor 120 are constructed and arranged to achieve a flow rate of blood of at least 0.3 L/min. In some embodiments, the system is configured to provide a flow rate of blood between 2.0 and 6.0 L/min. In some embodiments, the fluid flow system allows the speed to be set (e.g., automatically or manually) to a level between a minimum speed and a maximum speed. A typical speed of the impeller is several tens of thousands of revolutions per minute (rpm).
Areas of insufficient flow, such as low-flow areas within or proximate to the pump can result in circulated blood undesirably transitioning to solid matter. With blood pumping systems, blood in a stasis or near-stasis condition can transition to thrombus. Creation of a thrombus or other solid matter can result in reduced flow of blood through the pump or release of solid matter into the patient as an embolus.
For these and other reasons, there is a need for devices, systems and methods which reduce the potential for blood to stagnate and which may improve the washing of blood on a bearing surface of the pump, which can decrease the risk that blood will transition to solid matter.